Indexes for diagnosis support have been calculated by administering a diagnostic medicine (cardiac function diagnostic medicine) for diagnosing a cardiac function to a subject and analyzing an image obtained by imaging the subject. Examples of the diagnostic medicines include a radioactive medicine that accumulates in myocardium by nature (hereinafter, also referred to as a radio isotope (RI) medicine). Examples of the RI medicine include MIBG (3-iodobenzylguanidine), MIBI (technetium hexakis-2-methoxyisobutylisonitrile), and thallium chloride. For example, an index known as heart/mediastinum ratio (H/M ratio) can be obtained from an RI planer image obtained by detecting radioactivity from a subject administered with MIBG. The H/M ratio is obtained from a comparison between an average count value in the cardiac region and an average count value in the mediastinum region. The H/M ratio is used for diagnosis as well as evaluation of severity and prognosis for a subject with a cardiac disease (NPL 1 to NPL 3). The H/M ratio is also used for a nerve disease, to diagnose dementia with Lewy bodies (NPL 4).
MIBI is used to evaluate a myocardial lesion in cardiac diseases such as ischemic cardiac disease, heart failure, and cardiac sarcoidosis, by measuring a washout amount. In such a case, a myocardium washout rate (WR) indicating a rate of the RI medicine washed out from the myocardium is used as the index. The WR is obtained from count values in an early image captured in a first time period after the RI medicine is administered and count values in a late image captured in a second time period later than the first time period. For example, the H/M ratio may also be used for measuring an uptake amount of other radioactive medicines such as thallium chloride into the myocardium.
PTL 1 discloses a technique of preventing a difference from occurring among practitioners in the calculated H/M ratios.
Furthermore, a technique has been known that is effective when the H/M ratios respectively calculated from RI planer images captured in different imaging environments. More specifically, the difference between the H/M ratios due to the difference between the imaging environments is eliminated, so that the H/M ratios respectively calculated from RI planer images captured under different imaging environments can be compared with each other (NPL 5).